Electrical signals are often transmitted over cables such as coaxial or twisted pair cables. Such cables connect myriad devices located throughout the world one to another. For example, coaxial or twisted pair cables can connect computers to other computers, network switches to centralized servers, television stations to set top boxes in users' homes, mobile devices to computer docket devices, among many other configurations.
Coaxial cables conventionally include a core conducting wire surrounded by a dielectric insulator, a woven copper shield layer, and an outer plastic sheath. The concentric layers share the same geometric axis, and are relatively well suited for transmitting radio frequency signals due to their special dimensions and conductor spacing. To reduce the radiation from the transmitted signal, the copper shield layer is connected to ground, thus providing a constant electrical potential. Thus, radio waves are generally confined to the space between the conducting wire and the woven copper shield layer.
But traditional coaxial cable designs are subject to signal leakage, and in addition, losses or reductions in power. Signal leakage is caused by electromagnetic signals passing through the metal shield of the cable, and can occur in both directions. Metal shields are notoriously imperfect due to their holes, gaps, seams, and bumps. Making perfect metal shields is cost prohibitive and would make the cables bulky and exceptionally heavy.
Signals can be impacted by external electromagnetic radiation emitted from antennas, electrical devices, conductors, and so forth. Such interference can impact the quality and accuracy of signals that are transmitted over the cables. Errors introduced into the signals can range from generally mild effects such as video artifacts in a television signal, to more severe effects such as erroneous data transmitted to or from a critical device upon which human life depends.
Moreover, signal leakage can cause disruption to the signal being transmitted. In addition, noise can be leaked from the coaxial cable into the surrounding environment, potentially disrupting sensitive electronic equipment located nearby. Signal leakage also weakens the signal intended to be transmitted. In extreme cases, excessive noise can overwhelm the signal, making it useless.
Twisted pair cables conventionally include two wires that are twisted together. One of the wires is for the forward signal, and the other wire is for the return signal. Although twisted pair cables have certain advantageous properties, they are not immune to noise problems. Noise from external sources causes signals to be introduced into both of the wires. By twisting the wires, the noise produces a common mode signal, which can at least partially be removed at the receiver by using a difference signal.
However, such twisting method in itself is ineffective when the noise source is too close to the twisted pair cable. When the noise source is close to the cable, it couples with the two wires more effectively, and the receiver is unable to efficiently eliminate the common mode signal. Moreover, one of the wires in the pair can cause cross talk with another wire of the pair, which is additive along the length of the twisted pair cable.
Accordingly, a need remains for noise dampening coaxial and twisted pair cables capable of reducing unwanted electromagnetic interference from impacting the transmission of signals. In addition, a need remains for improving the power and energy efficiencies of coaxial and twisted pair cables. Embodiments of the invention address these and other limitations in the prior art.
The foregoing and other features of the invention will become more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.